This invention relates to a wavelength conversion element, and more particularly to the wavelength conversion element using non-linear optical material and to methods of manufacturing the wavelength conversion element.
Recently, a fiber state, or a so-called fiber type of wavelength conversion element has been proposed to obtain higher output of SHG (second-harmonic generation). This element has a cylindrical core section with an outside diameter of about 1 to 2 .mu.m and a clad member attached to the periphery of this core section with an outside diameter of about 1 to 2 mm. As material for the core section, organic non-linear optical material is used, while glass is used for the clad member.
Conventionally, the fiber type of wavelength conversion element as described above has been manufactured by making fused core material infuse into a glass capillary by means of capillary action and then crystallizing the material therein.
However, the fiber type of wavelength conversion element produced by using the glass capillary has various problems as described below.
At first, to optimize a wavelength conversion efficiency, the core diameter must be controlled at an order of sub-micron. However, with respect to manufacturing the wavelength conversion element, as the core diameter and the clad diameter are fabricated by heating and extending the capillary which is larger than the final dimensions of the wavelength conversion element to be manufactured, a control of the core diameter is extremely difficult.
Secondly, the wavelength conversion efficiency is in proportion to the so-called opperative length, and to obtain a high wavelength conversion efficiency, the fiber length must be made as long as possible, and also use of the fiber with a large clad diameter is required to prevent phase disturbance due to reflection of second harmonic at an interface between the clad and the air.
However, the ratio of core diameter to clad diameter is almost defined by the ratio of core diameter to clad diameter before extension by means of heating, and this ratio is about 1:1000, so that it is very difficult to obtain an extremely large diameter clad.
Thirdly, at both end faces of the wavelength conversion element, organic non-linear optical material in the core section is exposed to the air, which results in degradation of the material, and it is necessary to arrange a sealing layer on the end faces of the fiber to avoid this problem.